1. Technical Field
The present invention relates to a skew measurement apparatus, a skew measurement method, a recording medium, and a test apparatus. In particular, the present invention relates to a skew measurement apparatus, a skew measurement method, a recording medium, and a test apparatus for measuring skew of a plurality of signal under measurement using a digital comparator such as a voltage comparator.
2. Related Art
Skew refers to the timing difference between a plurality of signals output from a plurality of signal sources. Conventional skew measurement methods use a time interval analyzer or a frequency counter to statistically estimate the skew. For example, Wavecrest Corp., Jitter Analysis Clock Solutions, 1998 discloses an exemplary skew measurement using a time interval analyzer. As another skew measurement example, U.S. Pat. No. 7,127,018 discloses a technique for obtaining instantaneous phases of clock signals under measurement and obtaining the clock skew from the initial phase difference between these instantaneous phases.
The clock skew measurement method using the time interval analyzer, however, has dead time after each single measurement during which another measurement cannot be performed, and therefore a long sampling time is required to achieve the desired measurement accuracy. Since waveform measurement accuracy of approximately 8 bits is required to accurately calculate the initial phase of the instantaneous phase of the clock signal under measurement using the analysis technique disclosed in U.S. Pat. No. 7,127,018, this technique cannot be applied to a semiconductor test apparatus that samples a waveform with a 1-bit comparator.